1997 V6 3.4 with engine knock

HELP! A friend of mine has this truck I just looked at. :banghead:
The noise is not at an idle but starts at around 2k RPM, and is not as loud when revved in drive with brakes set.
The noise was not there when cold but after only about a minute of warm up, it started. Seems to be top end, driver side, not fuel rail, does not seem to be coming from the rocker covers, and no noise at all in the oil pan.
The noise was loudest with a stethoscope at the exhaust ports.
Any experience with this will be appreciated.
Thanks,
4Wheel

Is it louder front or back? or any particular cylinder?

How is the engine power? Exhaust appearance?

I think the noise is coming from the driver side of the engine (possibly cylinder #3). The engine does not make noise at idle, it however starts to get noisy once I rev up the engine. It is noisier when I go uphill as I have to push the engine harder. I do not seem to have lost a lot of power since I started hearing the noise.

Hi Brian,
Thanks, I have alerted him that there are questions and he is logging in for the first time I will let him field the questions from here on out.
I will keep watching and help where I can.
Thanks

He did say there was a degradation in MPG I didn't see any exhaust issues.

Exhaust manifold gasket leak? or crack in the manifold?

Sorry forgot to mention that it is a mechanical knock.
Just to hear it, sounds like a wrist pin or conrod bearing.

I had another mechanic check my car. I was told that there is carbon build up in the engine. The mechanic perfomed an emission system cleaning service which reduced the noise a lot. I was told to drive my SUV more to avoid this problem in the future.

Try running some GM Top Engine Cleaner or Seafoam through your intake.

(somewhere away from civilization since it will smoke a bit)